<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>获得字符串第 N 个位置的字符</title>
</head>
<body>
    <script>
        var a='4545454122121122235464565656'
        // charAt返回指定位置的字符
        var b=a.charAt(3)
        console.log(b)
	    
    </script>
</body>
</html>